1. The Field of the Invention
The present invention relates to an apparatus and methods for using the same in the fabrication of an integrated circuit, and particularly an apparatus for performing both a cleaning process and a scrubbing process upon a semiconductor substrate utilizing one machine that integrates the cleaning and scrubbing processes in the fabrication of an integrated circuit situated on a semiconductor substrate.
2. The Relevant Technology
In the context of this document, the term xe2x80x9csemiconductor substratexe2x80x9d is defined to mean any construction comprising semiconductive material, including but not limited to bulk semiconductive material such as a semiconductive wafer, either alone or in assemblies comprising other materials thereon, and semiconductive material layers, either alone or in assemblies comprising other materials. The term xe2x80x9csubstratexe2x80x9d refers to any supporting structure including but not limited to the semiconductor substrates described above.
Producing a substantially impurity free semiconductor substrate is an ongoing challenge during fabrication of operable integrated circuits and other microelectronic devices. During fabrication, several operations are completed with that require a thorough cleaning of the semiconductor substrate prior to any further processing.
Processes used to remove impurities from a semiconductor substrate include etching, cleaning, and scrubbing. A scrubber can be used after an abrasive operation such as a polishing process. Such abrasive operations can be mechanical or chemical mechanical. For example, after a chemical mechanical planarization (CMP) process has been completed, one or more contaminates can remain on a surface of a semiconductor substrate that was subjected to the CMP process. In this situation the contaminate is typically not completely removed with a wet-cleaning process alone. The extra cleaning power of a physical cleaner is needed. Scrubbers such as brush scrubbers are used to provide the needed physical cleaning action. The brush scrubber is not, however, used immediately after every CMP process. There are times when an intermediate cleaning step is utilized. One cleaning process that is regularly done prior to the scrubber cleaning process is some type of a cleaning process such as a wet-cleaning process.
A wet-cleaning process is particularly useful after semiconductor substrates have been processed on a polishing tool. A wet-cleaning process is needed between the CMP process and the scrubber because if the semiconductor substrates go from the polishers to the scrubbers, the scrubber tends to get loaded with polishing residuals. The polishing residuals are typically in the form of a slurry or abrasive media combined with particles from the portion of the semiconductor substrate that was removed by the polisher. A cleaning process such as a wet-clean process can remove a large portion of the polishing residue.
Current technology requires two separated work stations and machines for the cleaning process and the scrubber process. A semiconductor substrate must currently be loaded and unloaded for each of the two separated machines and be transferred therebetween. With each transfer of the semiconductor substrate between various machines used during fabrication, the possibility of contamination increases and with that, also the likelihood of lower process yield. As such, it would be advantageous to control the surface chemistry, the ambient humidity, the temperature, and the ambient particle contamination between the cleaning process and the scrubber process.
By way of example, a semiconductor substrate may have situated thereon a mixed interface of hydrophobic and hydrophilic material on a surface thereof. A batch of the semiconductor substrates is to be first processed in a wet cleaning machine and then processed in a scrubber machine that is proximally close yet separated from the wet cleaning machine. The separation of machines may, during transportation of the semiconductor substrates therebetween, cause some oxidizing or localized air drying of regions of hydrophobicity on the semiconductor substrates that can cause problems later on. Also, if the semiconductor substrates have a polishing residue thereon that, once dried will not scrub off, a nucleation site can develop that may later reduce fabrication yields and increase device failures. Extra precautionary measures are desirable in the fabrication process to try to reduce the potential contamination caused by the transfer of the semiconductor substrate between various separated machines. Such measures tend to reduce throughput.
Fabrication processes performed upon semiconductor substrates must be done in a tightly controlled environment, typically referred to as a clean room. Because of the closely controlled environment of a clean room and the expense and equipment required to maintain the conditions of the clean room, floor space is very valuable. At the same time, however, the increasing number of processes and innovations that require new or additional machines are competing for valuable space in the clean room.
As seen in FIG. 5, an exposed interface of silicon dioxide 54 and polysilicon 56 on a semiconductor substrate 50 was formed using a CMP machine. The CMP machine would leave slurry particles 55 as seen in FIG. 5 upon the exposed interface. Semiconductor substrate 50 would then be moved to a different machine that would perform a scrubbing process upon semiconductor substrate 50. The scrubbing process would remove slurry particles 55 as seen in FIG. 5, but would leave a cleaning solution droplets 62, 64 as seen in FIG. 7 upon the exposed interface. While cleaning solution droplets 64 are upon the hydrophobic polysilicon 60 and tend to bead up due to high surface tension, cleaning solution droplets 62 are upon the hydrophilic silicon dioxide 58 and tend to spread out due to the lower surface tension.
After the scrubbing machine, semiconductor substrate 50 would again be moved to a spin-dry machine, separate from the scrubbing machine, that would perform a drying process. The drying machine spins whiling drying semiconductor substrate 50. This process typically leaves water spots on the hydrophobic exposed surface of polysilicon 58. These water spots result in an oxidation of the polysilicon, leaving oxide 61. Oxide 61 causes problems in later processing, where an electrically conductive material is deposited over polysilicon 58 upon oxide 61. The oxidized portion 61 of polysilicon 58 causes an increase in resistivity between polysilicon 58 and the electrically conductive material thereover, leading to improper device performance and other defect-related reduction in performance characteristics.
Alternately, prior art processes have also oxidized an exposed surface of polysilicon of an exposed interface of silicon dioxide and polysilicon before the semiconductor substrate was dry or otherwise subjected to a drying process. The oxidation of the exposed polysilicon occurred either during the brush scrubbing process or could also occur even before the brush scrubbing process. Thereafter, the oxidized portion of the exposed polysilicon surface would be removed in a high-pH solution, such a solution of ammonium hydroxide and peroxide. This oxide removal process tended to also etch the polysilicon while still leaving a thin oxide on the polysilicon. Next, the wafer was dried in a spin rinse and dry process in which the oxide layer still remained and had not yet been removed. Consequently, a still further hydrofluoric acid etchant would be needed to remove the oxidation from the polysilicon.
As noted above, prior art processes moved the semiconductor wafer across distanced between multiple tools. Tools that integrated various processes have been suggested nor taught the combined tools of brush scrubbing with spin rinse drying. This present state of the art in such an integrated tool is known to cause water spots on hydrophobic surfaces such as polysilicon, and thus oxidation thereof
What is needed is a method of performing a cleaning process and a scrubbing process in such a way as to substantially eliminate contamination incident to semiconductor substrate transfer from machine to machine to perform the various operations. A device that will accomplish the improved cleaning method while utilizing less space in the clean room is also needed. It would also be advantageous to more efficiently clean semiconductor substrates after an abrasive process.
More particularly, there is a need for an integrated tool that uses brush scrubbing of an exposed polysilicon and silicon dioxide surface on a semiconductor substrate to remove therefrom silicon dioxide particles remaining from the slurry of an CMP process, followed by an operation within the same integrated tool that cleans the exposed polysilicon and silicon dioxide surface and achieves a final dry state thereof without creating water spots or oxidation of the exposed polysilicon surface.
The present invention includes a method for cleaning a semiconductor substrate, where a hydrophilic material on the semiconductor substrate is removed to expose an interface with a hydrophobic material. The hydrophobic material is oxidized while brush scrubbing the interface, after which the semiconductor substrate is moved away from the brush scrubbing into a gaseous ambient, and then into a cleaning bath. During the move, the hydrophilic and hydrophobic materials are unaffected. The oxide is removed from the hydrophobic material in the bath, and the location of the semiconductor substrate is changed to a gaseous ambient, and then to a dryer, where the hydrophilic and hydrophobic materials are unaffected during the change of location. The hydrophilic and hydrophobic materials are dried in the dryer without oxidizing the hydrophobic material. It is preferable that, during both the moving and the change the location, the ambient humidity, the ambient temperature, the ambient particle contamination, and the chemistry on the hydrophilic and hydrophobic materials are constant. Also, it is preferable that the hydrophilic material is silicon dioxide, and that the hydrophobic material is polysilicon.
In another embodiment, the inventive method uses an integrated cleaner with scrubber for cleaning and scrubbing semiconductor substrates. The integrated cleaner with scrubber includes a housing, a cleaning module, and a scrubbing module. The cleaning module is disposed within the housing. The cleaning module is capable of performing a cleaning process on a batch of the semiconductor substrates. The cleaning module comprises a cleaning tank, drain means for emptying the cleaning tank of a cleaning media, and supply means for providing the cleaning media. The cleaning module can also include a megasonic device associated with the cleaning tank.
The scrubbing module is also disposed within the housing. Either before or after processing takes place in the scrubbing module, one or more of the semiconductor substrates in the batch can be moved out of contact with the cleaning media in the cleaning module and into a gaseous ambient. Then, the one or more semiconductor substrates be moved to the scrubber module. The surface on each of the semiconductor substrates will be unaffected during the transportation thereof.
The scrubbing module is capable of performing a scrubbing process on one or more semiconductor substrates. The scrubbing module comprises a plurality of scrubbers and drive means for supplying power to the scrubbers. The integrated cleaner with scrubber also comprises a material handling means for removing a batch of semiconductor substrates from the cleaning module and for loading the semiconductor substrates individually into the scrubbing module without removing the semiconductor substrates from the housing of the integrated cleaner with scrubber. An optional drying device may also be integrated into the integrated cleaner with scrubber. The drying device drys the semiconductor substrates after the scrubbing process.
One embodiment of the inventive process uses an integrated tool having therein a brush scrubbing machine that is used on an exposed polysilicon and silicon dioxide interface to remove major silicon dioxide particles that remain upon the interface due to the slurry from a prior CMP operation that was used to expose the interface. In this embodiment, a wet cleaning process is performed upon the interface within the same integrated tool. The wet clean can use solutions of hydrofluoric acid (HF), HF with tetramethylammonium hydroxide (TMAH), or a buffered oxide etch. The wet cleaning process etches any remaining silica slurry particles while removing any native oxide from exposed polysilicon surface on the interface.
Finally, a drying process is conducted within the same integrated tool so as to achieve a final dry state of the exposed interface without creating water spots or oxidation of the exposed polysilicon surface on the interface and so preserve the surface states of mixed polysilicon and silicon dioxide exposed surfaces. The drying process can be a Marangoni-effect aqueous rinsing/drying process or an isopropyl alcohol (IPA) drying process.
These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.